Some wireless communication network protocols employ a random access channel for wireless communication devices to use when initiating wireless communications with a wireless access node. A wireless device attempting to initiate communications with the access node requests a communication channel over the random access channel using one of a fixed number of preambles for communications on the random access channel. Of the fixed number of preambles, a portion of the preambles is allocated as contention based preambles and the remainder of the preambles are allocated as contention free preambles.
If a wireless device is originating communications on the access node, then the wireless device uses a contention based preamble, which the device selects at random, to communicate over the random access channel. As the preamble is contention based, it is possible that another wireless device will attempt to use the same preamble to initiate communications. Thus, the access node employs a contention resolution procedure during times when multiple devices use the same preamble.
Alternatively, if the communications originated on another access node and are handing off to the access node, then the wireless device is assigned a contention free preamble that only that particular wireless device is able to use on the random access channel for communicating at that time. Contention free preambles allow a wireless device that is handing off to initiate communications with the new access node without the risk of adverse effects caused by a preamble collision.
While the number of wireless devices needing either contention based or contention free preambles may change over time, the portions of the total number of preambles on the random access channel allocated as each preamble type remains constant. Thus, at times, the demand for one type of preamble may not be satisfied by the constant preamble allocation.